Methyl-ethyl ketone dewaxing process



April 3, 1956 o. s. PoKoRNY ETAL 2,740,746

METHYL-ETHYL KETONE DEWAXING PROCESS Filed May l5, 1952 SEDAQAT l MG@RUM f f (2O [l 2i .1 ,Qll'gtvcgffv VAPOR, LIME \1\ @N fu' 1- 'n Y f(omnausEm.

` f WATER. 1Q" l OUTLET 5cm EMT l u E e) WASH F'l LTlzATE cam/EMTSTORAGE i2) ML TANK, i5 """.`;'k, KNIFE y t d 25 r2`7- ".5 ,f1/'I' 1 lpEuT WASH LQUD wAx ii 50u/EMT l SLUMY i8" Y LNE l f HEAT l Y 50W M ExdHAM@ El 10 6 J E TV TEAM A Ll E Tua y1' 5T T 95 R 50u/EMT 'Fraai 6FILTRATE 3L-VENT Qt-HLLESL c WAEHED WAx AnLE vd; fTorzAc-,E TAM. TAMLLStates 2,740,746 METHYL-ETHYL KE'I'ONE DEWAXING PROCESS This inventionconcerns the dewaxing of petroleum oil fractions and in particular thedewaxing of lubricating oil. In accordance with this invention aparticular ketone type solvent is employed as a dewaxing agent in amanner to substantially improve the character of the dewaxing operation.The solvent to be employed constitutes a mixture of a methyl-ethylketone type solvent with about 60 to 75 of diethyl ketone.

The present application is related to Serial No. 217,976 (now U. S.Patent No. 2,688,587, granted September 7, 1954), tiled March 28, 1951,for Oldrich S. Pokorny and George A. Speer. This application disclosedand claimed that particular portions of diethyl ketone when incorporatedin a dewaxing solvent containing a normal propyl group had the eect ofan anti-solvent for water. In some manner, 20 to 60% of diethyl ketoneserves to minimize harmful etects of water contamination of thealiphatic ketone solvent containing a normal propyl group. The presentinvention is based on the discovery that the antisolvent powers ofdiethyl ketone towards water can also be appreciated when employing amethyl-ethyl ketone type solvent, provided about 60 to 75% of thediethyl ketone is employed. The anti-solvent powers of the diethylketone then serve to improve the basic characteristics of themethyl-ethyl ketone dewaxing operation so as to decrease sensitivity towater contamination, to increase iilter rates, to decrease oilcontamination of the resulting Wax, and to permit attaining an oil of alow solid point at a higher operational temperature.

Since about 1930 one of the commercial processes for recovering Wax frompetroleum oils has been the ketone dewaxing process. While other ketonesmay be employed in this process, it has been the general practice toemploy methyl-ethyl ketone (in admixture with aromatics), as thesolvent, so that the process has generally been known as themethyl-ethyl ketone, or MBK dewaxing process. Commercial MEK dewaxingprocesses simply require the addition of a suitable quantity of the MEKsolvent to the oil to be dewaxedso as to permit complete solution of allwax present in the oil when the mixture is heated. After the wax hasbeen dissolved, upon cooling down the mixture of oil and ketone, ,thewax is precipitated and is removed from the oil by tiltration. While, asindicated, the MEK process has been in commercial use for a great manyyears, certain deticiencies of this process have become apparent. Forexample, it has been found that with certain types of oil stocks,extremely poor iilter rates are obtained, presumably due to theformation of wax crystals which are diicult to separate from the oil. Aconcomitant of this difficulty is that the oil content of the wax isgenerally at a level which is undesirably high, which in turn results inpoor yields of dewaxed oil. Consequently, it is the principal object ofthis invention to materially improve the ilter rates, to improve dewaxedoil yields, and to decrease the oil content of the wax obtained in theketone dewaxing process. For example, it has been found that due tominor portions of water contaminating the dewaxing solvent, poor iilterrates are obtained and it becomes diiiicult to obtain oil of a desirablylow pour point. Water contamination as ordinarily encountered incommercial operation furthermore results in a wax of a relatively highoil content and relatively poor yields of dewaxed oil. Consequently,

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it is the principal object of this invention to overcome thesedisadvantages of the methyl-ethyl ketone dewaxing process.

Throughout this disclosure, the solvent to be employed will be referredto as a ketone, or specifically as methylethyl ketone. However, it is tobe understood that any ketone containing from 3 to 6 carbon atoms may beemployed. Again, it is to be understood that the solvent consistingprimarily of a ketone of this class may also include up to 50%, or morecommonly, from 25 to 50% of an aromatic compound or compounds employedto favorably supplement the solvent action of the ketone. Benzene andtoluene are examples of aromatic constituents which may and often areincluded with the lower molceular weight ketones such as methyl-ethylketone `to provide the dewaxing solvent.

In'employing ketone type solvents of the nature described, the oil to bedewaxed is diluted with the solvent and is then heated to a suicienttemperature to dissolve all wax present in the oil. On cooling theoil-solvent-wax solution by use of heat exchanging, chilling surfaces,the wax is precipitated from the solution and may be recovered. The useof chilling surfaces or the external chilling of the solution is acharacteristic of the ketone dewaxing process.

In accordance with this invention, it has been found that the solventproperties of a methyl-ethyl ketone type dewaxing solvent may beadvantageously atiected by incorporation of about 60 to 75% of diethylketone. The resulting solvent composition consisting of this mixture ofdiethyl ketone and methyl-ethyl ketone is particularly desirable asregards the sensitivity of the solvent mixture for water contaminationduring the dewaxing operation.

In the conduct of commercial scale dewaxing of lubricating oils it isimpractical to completely exclude all water. Thus, for example, thedewaxing solvents employed generally contain small percentages of water,usualy between 0.2 to 0.5 volume percent, which may be due to steamdistillation employed in the inishing of these solvents. Again, thelubricating oil fraction to be dewaxed ordinarily is contaminated with alow percentage of water. Finally, water inevitably finds its Way intothe dewaxing apparatus and feed stream through accidental contamination.The principal sources of this Water contamination are:

1.` Water emulsion in the waxy feed stocks caused by sweating in thestorage tanks, leakage of steam used in heating coils employed toprevent crystallization of waxes, etc.

2. Recovery of the last traces of the dewaxing solvent from dewaxed oilor wax by steam stripping and re-usng this solvent in the dewaxing step.

The amount of water contamination which is ordinarily encountered isgenerally sutlicient to increase the Water content by 0.1 to 0.3 volumepercent per day of dewaxing plant operation.

The presence of contaminating water, even in quantities as low as 1% orless, exerts several undesirable functions. First and most important,the presence of water raises the miscibility temperature of the dewaxingsolvent and oil. This effect is so marked that the miscibilitytemperature of oil and methyl-ethyl ketone, for example, is raised 29 F.by the presence of 1% water. The result is that higher dewaxingtemperatures would have to be employed to avoid contamination of the waxwith oil precipitated from the solvent as a result of the presence ofwater.

In addition to this factor of adversely changing the miscibilitytemperature, or as a result of this factor, the filter rates which maybe maintained are seriously affected by water. This is presumably due toblinding of the ilter cloths by the oil which is precipitated out whenthe immiscibility point is reached. The eiiect of water contamination ondewaxing plant operation is shown by the following summary of dataobtained when using a mixture of methyl normal propyl ketone with methylnormal butyl ketone as a dewaxing solvent:

to use a continuous type of rotary filter. This consists of a drum 13,the cylindrical surface of which is covered with the filter cloth. Thedrum is mounted in a casing 14 on an axle, of Vwhich only the end 15 isshown.

Table l Charge Stock Filter Rate, US Percent Extracted: Percent Dewax-Dilu- Wash GaL/sq. ftJhr. Pour Dry Percent Mid- Water ing tion, Solvent,ASTM Wax Qll Continent in Temp., V. V. V./V. o F 1n in DistillateSolvent F. Feed Feed Waxy Dewaxed Feed Wax SAE Grade Feed O Stock 0.2 262.8 1. 8 5. 8 5. 1 +25 11. 6 11.0 0. 15 18 2. 8 2.0 4. 5 3. 9 +20` 12. 58.5 0. 2 20 2. 9 2. 2 4. 7 4. 1 +15 10. 8 6. 5 0. 8 19 2. 3 1. 9 4. 3 4.0 +15 4. 5 23 1. 1 20 2. 5 1. 9 3.9 3. 6 +15 4. 5 2S 1. 18 3. 5 1. 9 3.7 3. 2 +15 7. O 71 1. 0 24 3.6 2. 3 3. 4 1. 9 +20 6.5 88 0. 2 24 3. 4 2.3 2. 8 2. 5 i-20 9. 6 23 0. 29 3. 3 2. 6 3.1 2. 7 +25 10. 6 13 v`Theabove data bring out the disadvantages of waterV contamination indewaxingLresulting in large losses of oilinto the wax cake and inabilityto reduce the oil content of the wax even after re-pulping of the waxcake followed by a secondary de-oiling step. The wax finishing operationthus becomes more expensive if not, for practical purposes, impossible.Again, the effect of dewaxing under conditions'of incipientimmiscibility resulted in a loss of approximately 10% in dev/axing plantthroughput incurred largely due lto the more rapid blinding of thefilters, necessitating more frequent hot washing of the filter cloth.The oil content of the stripped wax also increased from 8 to 11% tobetween 16 and 28%.

In accordance with this invention, these disadvantages, brought about bycontamination of the dewaxing Voperation with water, may besubstantially avoided by including about 60 to 75% of diethyl ketone inthe methylethyl ketone dewaxing solvent. The dewaxing solvent thusconsists of any one or a mixture of C3 to Cs aliphatic ketones togetherwith about 60 to 75% of diethyl ketone. This solvent mixture mayincorporateV up to Vabout 50% of an aromatic compound or compounds tosupplement the solvent action of the ketones. A par'- ticularlypreferred dewaxing solvent composition for use in this invention iscomposed of about 23.8% of methylethyl ketone, 5.1% of benzene. 5.1% oftoluene and 60% of diethyl ketone. y

The manner in which the dewaxing-s'olvent composition. of this inventionis to be employed may be under stood by reference to theaccompanyingdrawing illusrtrating a diagrammatical flow plan of asuitable dewaxing operation.

The operation of a continuous filter is well known, and it need vonlybesaid that the drum is continually rotated at a low speed, usually ofthe order of 21/2 minutes per revolution. The liquid ywax slurry isintroduced at the bottom of the casing and filtration occurs on about 15to 40% of the circumference of the filter drum. The filtrate passesthrough theY cloth and finds its way out through one end of the axle 15,which is of course in the form of a pipe. A pipe 16 connected to the endof the axle conducts the filtrate to a storage tank 17. From the storagetank the filtrate is passedY to a steam still 18 Vfrom which the solventtogether withV steam passes overhead through vapor line 19 to acondenser 20. The solvent separates from the condensed steam in aseparator drum 21. Water is discarded by pipe 22 and solvent passes bypipe 23 and a pump 24 to the tank 5 for re-use.

As indicated above, about 15 to 40% of the circum` ference of the drumis continually in use for filtration, being directly submerged in thewax-solution mixture. During this period, wax cake is formed which canbe described as having a spongy structure, due to the inter locking ofWax crystals, in which the volume of voids filled with the solution isabout 6 to l0 times as great as is the volume of the crystallineparaffin wax which isdeposited on the filter blanket. This wax cakecontinuously moves into the sector (about 40 to 55% of thecircumference) in which it is .continuously Washed with VReferring tothe drawing, numeral 1 designates al 'storf oil by means of pipe 4 fromsolvent tank 5 through line 6. g In general this is' done to put theprocess in operation, but after the conditions have been settled to asteady state, the bulk of the fresh solvent isnot added directly to theoil but is supplied for washing'filter cake l as will be disclosedbelow, and the washings from the filter, called cycle solvent are addedto the oil to be dewaxed through pipe 4, as indicated. Y

The oil-solvent mixture isthen blended in the desired proportion,disclosed below, and is passed to heat exchangers S and 9, then througha chiller 10.V In the chiller the temperature is reduced to sucha'poi'nt thatrthe waxy content of the mixture is solidified and thedewaxed oil after removal of wax would be uid at the desired pourtemperature. Pipe 11 conducts this mixture of liquid constituents andsolid particles of wax to a filter shown generally at 12. The filtermay, of course, be an ordinary plate and frame type, but it is preferredfresh pre-cooled solvent. The pre-cooled solvent which is used as awashing liquor is drawn directly from tank 5. by a pump 2S and entersthe filter casing at the top where it is distributed into 4 to 6 sprayor drip pipes which distribute the wash solvent uniformly over the waxcake surface.

' In the washing cycle about 25 to 35% of the solution retained in thevoids of the wax cake can be displaced by the wash solvent withoutchanging the concentration of the oil in the filtrate. The filtrate fromthe Washing cycle is therefore split into two fractions. The firstfraction, amounting to between 25 to 35% of the total solution in thewax cake, can easily be displaced, which is Videntical in composition tothe main bulk of the filtrate obtained during the -submergence orfiltration cycle, and is passed to the filtrate tank. The secondfraction which has a substantially lowery concentration of oil thanthemainrbulk of the filtrate, lis `generally Ycalled cycle solvent andis used forV diluting the incoming waxy charge.- It will bc understoodthaty some admixture of the filtrate and of the washing liquor isunavoidable in the commercial Vtype 'rotary lters even though the'axleof the filtering drum indicated by the filtrate passing out of the axleat one end, while the wash liquor or cycle solvent is removed from theopposite end.

The wash liquor ows through a pipe 27 to the heat exchangers 9 and 8,and then passes through a pipe 7 and is mixed with the original waxyfeed passed through the pipe 4. As stated before, fresh solvent is notcommonly used for diluting the waxy stock but is supplied chiey forwashing the wax cake only.

However, when rotary filters operate at filter speeds of the order of 2minutes per revolution, the hydraulics of the filter design necessitatethe adjustment of the slide valve which makes it inevitable that anincreased volume of wash liquor or cycle solvent is included in thefiltrate. The volume of cycle solvent available is then insuicient formaintaining the desired dilution and when this occurs, the differencemust be made up by the fresh solvent from a solvent tank 5. The basicprinciple which governs the filter operation is to regulate theseparation of the filtrate and cycle solvent (wash liquor) so that notmore than to 20% of the dewaxed oil is recycled in the dewaxing plantwith the solvent used for diluting the waxy feed stock.

The total filtering cycle, i. e. time required for filtration,

l washing, drying and blowing or removing the wax cake,

is not materially lengthened by using a relatively large quantity ofsolvent for washing the wax cake, as the filtering rate of the freshsolvent towards the end of the wash cycle becomes very high. By applyingall or most of the fresh solvent as wash solvent, it is possiblehowever, to produce a wax having very low oil content, while the yieldof dewaxed oil is close to the theoretical yield. That is, with anoverall dilution of 2.0 to 3.0 parts of solvent to 1.0 part of waxystock, it is possible to obtain a greater yield of dewaxed oil.

The washed wax cake is carried over into a removal zone, in which thecake is scraped from the filter blanket by means of a suitable doctorknife, and then slides into a trouh fitted with a screw conveyor. It iscollected at 28.

The wax cake removed from the filter contains about 6 parts by volume ofsolvent per unit volume of parain wax. While the solvent to wax ratiocan be somewhat reduced by a more prolonged drying on the lter, thiswould result in a lower throughput. If desirable, a larger reduction canbe effected by repulping the Wax cake by means of a centrifugal pump ora mixer and conveying the wax slurry to another rotary filter similar tothose used for the dewaxing operation. If desirable, the wax slurry isheated to between 60 and 95 F. before filtration to permit de-oiling atelevated temperatures. The removal of low melting point waxes in thede-oiling step materially aids the sweating operation or facilitates themanufacture of micro crystalline waxes from heavy lubricating oildistillates and residual oils. The solution thus removed might berecycled back as dilution, while the wax cake is collected and sent tothe solvent recovery plant.

It will be understood that the dewaxing operation, that is, themechanical separation of the wax from solution, may be accomplished byother means than by filtration. While filtration is perhaps the mostadvantageous mechanical means to separate the precipitated wax from thesolution, centrifuges may also be employed. This method is, however,inefficient and much less desirable than the previously describedremoval of wax by continuous filtration.

As indicated, the dewaxing solvent to be employed comprises a mixture ofdiethyl ketone with methyl-ethyl ketone or other Ca to Cs aliphaticketones. Benzene, toluene or other aromatics may be included in minorportions. The quantity of solvent to be used per volume of waxy oil willvary considerably depending upon the viscosity of the oil, the waxcontent, and the desirability of preparing commercial grades of wax fromthe wax cake formed on the filter. In general, it is possible to useless solvent with the lighter distillates than with the heavier oils.The total amount of solvent used, including that for washing, may be aslow as one volume of solvent per volume of waxy oil. With heavier oils,or if it is desirable to produce wax -substantially free of oil, it ispreferable to use from 21/2 to 3 volumes of solvent per volume of oil.It is rare that more than 31/2 volumes of solvent are required, althougheven larger amounts than this may be advantageous when the wax contentof the oil substantially exceeds 15 to 20%, chiey to increase the uidityof the wax slurry charged to the continuous filter-s.

The ltration rate in continuous rotary filters with these solvents willalso vary with the viscosity of the oil, but even in the case of veryviscous residual oils and cylinder stocks it is possible to obtainfilter rates in excess of 3.5 gallons of waxy oil per square foot oflter area. The separation between oil and wax is remarkably sharp, andwhile in most cases the pour point of the oil from the filtrate is thesame as the dewaxing temperature, it is found that it is even possibleto obtain pour points from l0 to 15 F. below the dewaxing temperature.

In considering the desirability of employing diethyl ketone in thesolvent compositions described, the following data is significant. f Theeffect of water on the solubility of a typical lubricating oil fractionemploying a variety of dewaxing solvents was determined. In theseexperiments the lubri eating oil fraction selected was a Mid-ContinentSAE- lubricating oil. This oil was diluted with three parts of differentsolvents having the compositions indicated in the following table.solvent-oil mixtures was determined for the anhydrous solventcompositions and for .5%, 1%, 1/2%, and 2% water contamination. The datais tabulated in the following table:

Table Il Composition of Dewaxnig Solvent Mlseibility Temp. ln F. AfterAdding- Percent Methyx- Percent Percent gigi@ 0% 0.5% 1% 1.5% 2.0% EthylBenzene Toluene Ketone Water Water Water Water Water Ketono 90 l0 39 5367 8l 94 75 25 27 42 57 70 83 60 40 15 31 46 60 73 60 -2 l5 31 46 49 2575 1 15 l 7 18 85 26 40 54 68 82 70 ll 27 27 27 2 63 l0 9 25 25 25 52. 525 7 16 16 16 5 42 40 -l +2 +2 +2 l 51 40 2l 35 48 23.8 -5 5 -6 -6 1 Themethyl-ethyl ketone-aromatics portion consists of 85% methyl-ethylketone, 7.5% benzene, 7.5% toluene.

2 The methyl-ethyl ketone-aromatlcs portion consists o! 70% methyl-ethylketone, 16% benzene. 16% toluene.

The miscibility tempera-ture of theV As indicated in the precedingtable, employing anhydrous methyl-ethyl ketone, the Mid-Continentlubricating oil employed could not be reduced to a pour pointsubstantially below about 46 F. without encounteringV conditions ofimmiscibility. Furthermore, when pure methyl-ethyl ketone wascontaminated with the quantities of water shown in the table, theanti-solvent action of the water resulted in an even poorer solventpower. Thus, for example, with 1% of water in methyl-ethyl ketone, themiscibility temperature of the oil solvent mixture was 75 F. However,when 60% of diethyl ketone is added to methyl-ethyl ketone, themiscibility temperature of this solvent mixture and the lubricating oilemployed was sharply dropped. Thus, for this solvent composition, 0.5%of water may be tolerated while permitting attaining a miscibilitytemperature of only 15 F. An even greater improvement is attained byemploying 75 of diethyl ketone. Y

A substantially anhydrous mixture of 85% methylethyl ketone, 71/2%benzene, and 71/2% toluene is required to dewax the lubricating oildistillate at 26 F. to provide an oil having a solid point of about 26F. However, by incorporating substantial portions of diethyl ketone, thedata again shows that substantially greater (to 0.7%) watercontamination of the solvent may be tolerated when dewaxing at the sametemperature for the same solidil'lcation point.

When a mixture of 70% methyl-ethyl ketone, 15% benzene, and 15% tolueneis used in dewaxing Mid- Continent SAE-30 grade distillate to a solidpoint of 0 or F., the solvent must be substantially anhydrous orconditions of oil-solvent immiscibility will be encountered. However,when about 40% diethyl ketone is added to this solvent, 2% or more watercan be tolerated, and conditions of oil-solvent immiscibility will Ynotbe experienced.

The following examples illustrate the use of these mixtures for dewaxingextracted Mid-Continent SAE-3() distillate diluted with 3 volumes `ofthe solvent, chilled at a controlled rate and filtered to remove thewax.

the dewaxing temperature. The follow-ing table shows;l thatthesolubility of wax in a solventconsisting of di ethyl ketone alone isabout equivalent to that in a conventional MEK solvent consisting of 70%methyl-ethyl ketone, 15% benzene and 15%` toluene, and is slightlygreater than the solubility of the wax in a mixture of methyl-ethylketone and 60% diethyl ketone. Hence, the use of diethyl ketone inmixture with methyl-ethyl ketone-aromatics dewaxing solvents will nothave an ad- What is claimed is: Y

1. Process ofdewaxing mineral oil which comprises diluting the oil witha solvent comprising methyl-ethyl ketone and about Y60 to 7 5% byvolume, based on the total solvent, of'diethyl'ketone, therea terchilling the mixture to a temperature at which wax is caused toprecipitate, removing thewax and recovering dewaxed oil from thefiltrate.

2. The processdened by'claim l in which the said solvent includes up toabout by volume, based on said methyl-ethyl ketone, of an aromatichydrocarbon chosen from the group consisting of benzene kand toluene.

3. A dewaxingv solvent composition comprising methylethyl ketone inadmixture with about 60 to 75% by 40 volume of diethyl ketone based onthe total solvent.

Table III Waxy Dist. Filter Rate) Solvent Composition Ig? 't lro Dewx-Dewafl ohnnng Rate ofiu O11 Solidi- Temg iication o p" Point,lirerriienit P t P t Pelrnc'ent F' F e y el'Cll elCeIl l- Ethyl BenzeneToluene ethyl 2 F'Mm' 5 F'Mm' Ketone Ketonc volume percent, Wax cakeapproximately 15% oil.

2 Methyl-ethyl ketone-benzene-tolucne portion ot these solvents consistoi 70% methylethyl ketone, 15% benzene, 15% toluene.

These examples indicate that, within the limits of experimental error,the addition of diethyl ketone to the mixture of methyl-ethyl ketone andaromatics does not aiect the filter rate obtainable with themethyl-ethyl ketone and aromatics mixture alone.

As illustrated above, it is not possible to dewax Mid- Continent SAE-30distillate using methyl-ethyl ketone below about F. (assuming the watercontent of the solvent to be 0.3% which is normally encountered incommercial plants) without experiencing a condition of immiscibility ofthe oil and solvent. However, when from to 75 volume percent of diethylketone is added to the methyl-ethyl ketone, this distillate may besuccessfully dewaxed at approximately +l0 F. at a higher filter ratethan with diethyl ketone alone.

Solidication points of dewaxed oils obtained from the liltrations of theabove table are equal to or lower Ythan 4. A dewaxing solventcomposition consisting essentially of methyl-ethyl ketone in admixturewith about 60 to 75% by volume, based on the total solvent, of diethylketone including up to about 50% by volume, based on the methyl-ethylketone of a solvent selected from the group consisting of toluene andbenzene.

5. A lubricating oil dewaxing process which comprises admixing the oilwith a solvent consisting essentially of up to 40% by volume, based onthe total solvent, of methyl-ethyl ketone, up to about 50% by volume,based on said methyl-ethyl ketone, of an aromatic hydrocarbon selectedfrom the group consisting of benzene and toluene, and in the range ofabout V60-75% by volume based on the total solvent of diethyl ketone,thereafter chilling the said oil-solvent mixture to a temperature atwhich wax is caused to precipitate, removing the wax and recoveringdewaxed lubricating oil.

1. PROCESS OF DEWAXING MINERAL OIL WHICH COMPRISES DILUTING THE OIL WITHA SOLVENT COMPRISNG METHYL-ETHYL KETONE ABOUT 60 TO 75% BY VOLUME, BASEDON THE TOTAL SOLVENT, OF DIETHYL KETONE, THEREAFTER CHILLING THE MIXTURETO A TEMPERATURE AT WHICH WAX IS CAUSED TO PRECIPITATE, REMOVING THE WAXAND RECOVERING DEWAXED OIL FROM THE FILTRATE.
 3. A DEWAXING SOLVENTCOMPOSITION COMPRISING METHYLETHYL KETONE IN ADMIXTURE WITH ABOUT 60 TO75% BY VOLUME OF DIETHYL KETONE BASED ON TEH TOATL SOLVENT.